Endodontic instrument for drilling the root canals of a tooth

ABSTRACT

An endodontic instrument for drilling the root canals of a tooth. The instrument comprises a working area for forming and/or shaping and/or cutting the wall of the root canal of the tooth. The working area is provided with a supporting endpiece that can be attached to a manual or mechanically driven mounting. The working area is arranged so as to assume a stowed configuration when the instrument is in an inoperative position to the working position, and vice versa, being cause by a predetermined variation in the temperature of the instrument. To this end, the working area is made from a wire of a metal alloy having shape-memory properties or particular elasticity properties.

This application is a national stage completion of PCT/CH2011/000296 filed Dec. 12, 2011 which claims priority from Swiss Application Serial No. 2100/10 filed Dec. 16, 2010

FIELD OF THE INVENTION

The present invention concerns an endodontic instrument, particularly an instrument for drilling a root canal in a patient's tooth, the instrument having a longitudinal axis and comprising a working area for forming and/or shaping and/or cutting and/or cleaning the wall of the root canal of the tooth, the working area being equipped with a supporting end piece that can be attached to a mounting.

BACKGROUND OF THE INVENTION

Cleaning and preparing root canals of a tooth for receiving filling material is accomplished using drilling instruments with an active portion called the working portion, the purpose of which is to shape and clean the root canal in preparation for receiving the materials used to treat and fill it.

Root canals often have specific shapes with complex curves and narrow cross-sections formed of constricted or oval areas that do not lend themselves to the introduction of preliminary shaping instruments. This is why instruments known as files must have characteristics that sometimes are contradictory: the files must be fine but resistant, yet flexible enough to conform to the curves of the root canal and reach the end of the canal, while nevertheless remaining durable enough to shape and cut the walls of the canal.

These exigencies oblige the odontologist to undertake a preparatory root canal treatment process using a broad array of tools and working progressively to adapt to the root canal morphology, the array of tools having various structures and dimensions. The intervention begins with a flexible fine instrument which will then be replaced by instruments of increasing cross-section until the root canal has an interior cavity large enough to receive the filling material. This is a long, delicate series of operations, being mindful that for safety reasons, the treating and filling material must completely fill the root canal and taking precautions to ensure that no residual air remains at the base of the cavity created in order to prevent any growth of bacteria and eventual infection.

These instruments are difficult to introduce into the root canal. In addition, to date there is no universal instrument adapted to the morphology of the root canal to be treated which would perform all the preparatory operations in one procedure. There is a risk of instruments cracking, becoming blocked in the canal, or greatly over-heating, which may cause breakage. This risk is notoriously present when using mechanically driven instruments made of nickel-titanium alloy, which wear out and must be carefully monitored by the odontologist throughout use. There is no doubt that using several different instruments in succession increases not only the cost of the intervention, but the complexity of the odontologist's work and risk to the patient.

U.S. Publication No. US2010/0233648 describes an endodontic instrument made of superelastic material which has one shape when introduced into the root canal and assumes a second shape when located inside the canal. This shape modification is linked to the superelastic properties of the material, allowing the instrument to undergo deformations when the shape of the canal imposes mechanical constraints.

International Patent Application Publication No. WO 2005/070320 also describes an endodontic instrument made of superelastic material with shape memory properties which can change shape during use due to mechanical constraints imposed by the walls of the root canal.

These embodiments are influenced by mechanical constraints, but they do not constitute cutting files which follow and respect the shape of the root canal as they bore into it.

SUMMARY OF THE INVENTION

The present invention proposes overcoming the disadvantages listed above and furnishing a means for ensuring effective root canal preparation by placing at the disposal of the practitioner an adaptable instrument which is easily introduced into the root canal, but nevertheless is shaped to prepare the canal adequately for treatment and filling.

This objective is achieved by the instrument of the invention characterized in that at least the working area is designed to have a retracted, at least partially rectilinear shape when the instrument is in inoperative position, with the instrument being in what is known as the martensitic phase, and an expanded structured shape adapted to the shape of the root canal when the instrument is in the operative position, with the instrument then being in what is known as the austenitic phase; the passage from the martensitic to the austenitic phase being triggered by a first predetermined temperature variation in the instrument and the instrument's return from its austenitic to its martensitic phase being triggered by a second predetermined temperature variation in the instrument.

Advantageously, at least the first predetermined variation in instrument temperature is triggered during the instrument's use after its introduction into the root canal.

Preferably the first predetermined variation in instrument temperature is a temperature elevation.

The temperature elevation, which triggers passage from the martensitic to the austenitic phase, falls within the range of temperatures comprising from 0° to 60° and preferably from 25° to 40° C.

According to a preferred embodiment, the second predetermined variation in the instrument temperature is a temperature decrease.

The temperature decrease to a temperature called the transformation temperature, which advantageously triggers the passage from the austenitic to the martensitic phase, falls within a range of temperatures comprised of from 60° to 0° and preferably from 45° to 25° C.

Advantageously at least the working area may be made of a metal alloy having shape memory properties that allow it to assume a retracted shape when at ambient temperature and an expanded structured shape at a higher temperature at the time of or after its introduction into the root canal.

In an especially advantageous manner, the metal alloy with shape memory properties is an alloy selected from the following alloys: nickel-titanium, copper-zinc-aluminum-nickel, copper-aluminum nickel, or zinc-copper-gold-iron or a combination of at least two of these alloys.

Depending upon its use, the expanded structured shape may be twisting, generally flat and auger-shaped, or corkscrew shaped and generally circular in section.

For specific uses, when in the expanded structured shape the instrument's working area may have portions comprising cutting edges or smoothing edges or an abrasive surface or at least one end section forming an angle with the axis of the instrument.

Depending on the variation, in the structured shape the working area of the instrument may be tubular and comprise two end sectors forming an angle relative to the axis of the instrument, the two sectors describing a cone during axial rotation by the instrument.

When the instrument is made of a flexible metal alloy, the instrument is designed to resume its retracted shape through a mechanical action after it has been used in the expanded structured shape.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and its principal advantages will be more apparent from the description of various embodiments, with reference to the attached drawings, in which:

FIG. 1A represents an instrument according to the invention in the shape of a flat auger at the time of its introduction into the root canal of a tooth;

FIGS. 1B through 1D represent the instrument of FIG. 1A after introduction into the root canal of the tooth, with FIGS. 1C and 1D respectively representing cuts in the tooth along axes 1C-1C and 1D-1D.

FIGS. 2A and 2C represent another type of embodiment of the instrument of the invention at the time of its introduction into the canal of the root a tooth, with FIG. 2C representing a cut into the root of the tooth along axis 2C-2C;

FIGS. 2B and 2D represent the instrument of FIG. 2A after introduction into the canal of the root of a tooth, with FIG. 2D representing a cut into the root along axis 2D-2D;

FIGS. 3A and 3C represent another variation of an expandable instrument according to the invention in a first operating state in the root of a tooth, with FIG. 3C representing a cut into the root along axis 3C-3C;

FIGS. 3B and 3D represent the instrument called the expandable instrument in FIG. 3A in a second operating state, with FIG. 3D representing a cut into the treated root of the tooth along axis 3D-3D;

FIGS. 4A and 4B represent an expandable instrument similar to that in FIGS. 3A through 3D in a different working configuration in the root of a tooth, with FIG. 4B representing a cut into the root along axis 4B-4B;

FIG. 5A illustrates a variation of the instrument of the invention called a tubular instrument introduced into the root of a tooth but in the inoperative position;

FIG. 5B is an enlarged view of the extremity of the working area of the instrument of FIG. 5A in inoperative position;

FIG. 6A illustrates the instrument of FIGS. 5A and 5B in the operative position inside the root of the tooth; and

FIG. 6B is an enlarged view of the extremity of the working area of the instrument of FIG. 5A in the operative position.

DETAILED DESCRIPTION OF THE EMBODIMENT

The instrument represented by FIGS. 1A through 1D is a manual type of instrument designed to be affixed to the extremity of a handle allowing the practitioner to scrape the generally oval root canal of a patient's tooth essentially using back and forth movements and pivoting movements around the instrument's longitudinal axis. The instrument 10 comprises a working area 11 made of metal wire comprising one or more strands extending into a supporting end piece 13 held by a mounting 14, in this case a handle allowing the practitioner to manipulate the instrument. FIG. 1A represents instrument 10 in the position of introduction into root canal 21 of a tooth 20. In this position, working area 11 of instrument 10 is in what is called the retracted position, in this case, generally rectilinear, which facilitates its introduction into root canal 21 and lets it pass easily through narrowing 16 visible in the canal. At ambient temperature, working area 11 maintains its retracted generally rectilinear configuration because of the metal alloy it is made of that has a property known as “shape memory.” This quality, known in itself, permits a suitable metal alloy to have a first geometric shape in a given range of temperatures and to assume a different geometric shape after passing to another temperature. In this case, working area 11 of the instrument, made of nickel-titanium based alloy, is generally rectilinear at ambient temperature, for example from 0 to 35° C., preferably between 10 and 30° C. and especially of the order of 20° C., and it assumes an expanded structured configuration at a higher temperature. At “low” temperature the material is in a phase called “martensitic” and its shape is relatively flexible, facilitating introduction of the instrument into the root canal. At a higher temperature, the material enters a phase known as “austenitic” and the instrument assumes a structured configuration allowing it to shape the canal walls, regardless of the canal's shape. To bring the material from its martensitic to its austenitic phase, depending upon the materials, a first temperature variation is applied, such as an elevation, located within a range of temperatures from 0° to 60° C. and preferably from 25° to 40° C. To return the material from its austenitic to its martensitic phase, depending upon the materials, a second temperature variation is applied, such as lowering the temperature to a value called the transformation value, situated within a range of temperatures extending from 60° to 0° C. and preferably 40° C. and 25° C. for certain nickel alloys. Alloys that are useful for their memory properties are principally copper-zinc-aluminum-nickel, copper-aluminum-nickel and zinc-copper-gold-iron alloys. Obviously other alloys with similar properties could be used.

The temperature increase can be accelerated using heating means incorporated in the instrument base or using exterior means such as, for example, sodium hypochlorite (NaOCl) which is used to disinfect the root canal. This compound may be injected through a heating syringe currently used by practitioners in the field.

The expanded structured shape assumed by working area 11 of instrument 10 is shown in FIGS. 1B through 1D. Working area 11 in this exemplary embodiment assumes the shape of a flat auger essentially filling the entire space of root canal 21 as shown in FIGS. 1C and 1D. This auger is extremely flexible so that it adapts to the shape of canal 21. In narrow portion 16 of the canal, loops 17 on the auger are less pronounced than in enlarged sectors 18 and 19, corresponding to the bottom and the entry to canal 21, respectively.

FIGS. 2A through 2D represent an instrument 10 according to the invention, of the mechanically driven type, engaged in one of canals 21 of a molar type tooth 20 with two root canals. In FIGS. 2A through 2C, working area 11, in its retracted configuration, is generally rectilinear, allowing easy introduction into root canal 21. In FIGS. 2B and 2D, working area 11 has assumed its expanded structured configuration following a temperature increase resulting either from contact with the patient's body or from a heating resistor (not shown) present in mounting 14 that supports instrument 10. In the example shown, the instrument is mechanically rotated and when in its structured state, it is shaped like a corkscrew. Working area 11 on instrument 10 is also of sufficiently flexible consistency that its cross-section can adapt to the cross-section of root canal 21, which is more or less conical. For this reason working area 11 is made with a metal alloy wire with shape memory that assumes its expanded structured configuration following a temperature elevation or a temperature change. The wire may be generally circular or perhaps angular in cross-section such that the instrument functions as either a smoothing, cutting, or abrasive tool according to the result desired. The practitioner may use several instruments with different or complementary functions depending on the initial shape of the root canal to be treated.

FIGS. 3A through 3D represent another embodiment of an instrument according to the invention of the mechanically driven type. This instrument 10, called an expandable instrument, has specific characteristics allowing it to adapt to the shape and dimensions of a root canal or “machine” the canal to give it the shape and dimensions desired for the subsequent root canal treatment. Instrument 10, in the state represented in FIGS. 3A and 3C, is introduced into one of the root canals 21 in tooth 20. This canal comprises a slight bulge 21 a in its central portion, followed by a narrowing 21 b. Working area 11 on instrument 10 adapts to this configuration. Like the instrument illustrated in FIGS. 2A through 2D, this instrument is mechanically rotated by its mounting 14 and depending upon the cross-section of the metal wire constituting it, its action produces either machining, cutting, abrasion or smoothing of the walls of root canal 21. In the present case, the goal is to enlarge the upper portion of the canal while eliminating narrowed portion 21 b in order to facilitate introduction of the filling substance. To do this, instrument 10 dilates, assumes the shape of a corkscrew with a generally circular cross-section, and acts on the walls by cutting or eroding the material of the tooth body, as shown in FIGS. 3B and 3D.

In the embodiment shown in FIGS. 4A and 4B, expansion of instrument 10 occurs essentially in upper portion 30 of working area 11 and the objective is to shape root canal 21 into a cone. Working area 11 may be a cutting, abrasive or smoothing one depending on what shape is contemplated for canal 21.

FIGS. 5A and 5B illustrate another embodiment of instrument 10 in which working area 11 is generally tubular and has a twisted appearance. Lower extremity 12 of this working area 11 is split axially for a certain length and comprises two sectors 12 a and 12 b that are visible in FIG. 5B. When the working area (whose extremity 12 is enlarged in FIG. 5B) is in the inoperative position, the two sectors 12 a and 12 b are juxtaposed in the axial extension of the rest of working area 11. Introducing the working area of instrument 10 into root canal 21 is easy because of its tubular rectilinear configuration. In its working position shown in FIG. 6A and 6B, lower extremity 12 has opened following a temperature elevation by virtue of the shape memory properties of the alloy forming the instrument, and the two sectors 12 a and 12 b form an angle between them that describes a more or less open cone when the tool is rotated by its turning mounting 14. The odontologist's objective is to create an enlarged cavity 22 at the extremity of root canal 21, the cavity being destined to receive the filler paste and prevent entrapment of air microbubbles at the canal base. Air microbubbles actually contain oxygen which can feed bacteria and decay, producing a more or less long term infection.

The present invention is not limited to the embodiments described, but may undergo different modifications or variations. In particular, despite the fact that the variations described are manual and mechanically driven, it is also possible to use ultrasonic vibrations to control the instrument. Additionally, depending upon the forms selected, preparation of the root canal may vary. These variations may also be obtained by adaptations in the shape of the metal wire the instrument is made of, the shape possibly being smooth or sharp, round or angular, etc. 

1-14. (canceled)
 15. An endodontic instrument, particularly an instrument for drilling a root canal in a patient's tooth, the instrument (10) defining a longitudinal axis and comprising: a working area (11) for at least one of forming, shaping, and cutting a wall of a root canal (21) of a tooth (20), and the working area (11) being equipped with a supporting end piece (13) that is attachable to a mounting (14), at least the working area (11) having a retracted configuration that is at least partially rectilinear in shape, when the instrument (10) is in an inoperative position, the instrument being in a martensitic phase, when the instrument is in a working position, an expanded structured configuration of the working area (11) adapting to a shape of the root canal with the instrument then being in an austenitic phase, and passage from the martensitic phase to the austenitic phase being triggered by a first predetermined variation in a temperature of the instrument, and a return of the instrument, from the austenitic phase to the martensitic phase, being triggered by a second predetermined variation in the temperature of the instrument.
 16. The endodontic instrument according to claim 15, wherein at least the first predetermined variation in the temperature of the instrument is triggered during use of the instrument after introduction into the root canal.
 17. The endodontic instrument according to claim 16, wherein the first predetermined variation in the temperature of the instrument is a temperature elevation.
 18. The endodontic instrument according to claim 17, wherein the temperature elevation that triggers passage from the martensitic phase to the austenitic phase occurs in a temperature ranging from 0° to 60° C.
 19. The endodontic instrument according to claim 17, wherein the temperature elevation that triggers passage from the martensitic phase to the austenitic phase occurs in a temperature ranging from 25° to 40° C.
 20. The endodontic instrument according to claim 15, wherein the second predetermined variation in the temperature of the instrument is a temperature decrease of the instrument.
 21. The endodontic instrument according to claim 19, wherein the temperature decrease to a transformation temperature, which triggers passage from the austenitic phase to the martensitic phase, occurs in a temperature ranging from 60° to 0° C.
 22. The endodontic instrument according to claim 19, wherein the temperature decrease to a transformation temperature, which triggers passage from the austenitic phase to the martensitic phase, occurs in a temperature ranging from 40° to 25° C.
 23. The endodontic instrument according to claim 15, wherein at least the working area (11) is made of a metal alloy having shape memory properties allowing the working area (11) to assume a retracted configuration, at ambient temperature, and an expanded structured configuration, at a higher temperature, either at the time of or after its introduction into the root canal (21).
 24. The endodontic instrument according to claim 23, wherein the metal alloy with shape memory properties is an alloy selected from a group of alloys consisting of: nickel-titanium, copper-zinc-aluminum-nickel, copper-aluminum-nickel, or zinc-cooper-gold-iron or a combination of two or more of these alloys.
 25. The endodontic instrument according to claim 15, wherein the working area (11) on the instrument (10), in the expanded structured configuration, has a twisted shape.
 26. The endodontic instrument according to claim 15, wherein the working area (11) on the instrument (10), in the expanded structured configuration, has a generally flat auger shape.
 27. The endodontic instrument according to claim 15, wherein the working area (11) on the instrument (10), in the expanded structured configuration, has a generally circular corkscrew shape.
 28. The endodontic instrument according to claim 15, wherein in the expanded structured configuration, the working area (11) on the instrument (10) comprises portions with one of at least one cutting edge, at least one smoothing edge, at least one abrasive surface, and at least one end section forming an angle with the longitudinal axis of the instrument.
 29. The endodontic instrument according to claim 15, wherein the working area (11) on the instrument (10), in the expanded structured configuration, is tubular and comprises two end sections (12 a, 12 b) forming an angle relative to the longitudinal axis of the instrument, and the two end sections are designed to from a cone during axial rotation by the instrument (10).
 30. The endodontic instrument according to claim 15, wherein the working area (11), after the working area (11) is used in the expanded structured configuration, resumes the retracted configuration through a mechanical action.
 31. An endodontic instrument for drilling a root canal in a tooth of a patient, the instrument (10) defining a longitudinal axis and comprising: a working area (11) for at least one forming, shaping, and cutting a wall of the root canal (21) of the tooth (20), and the working area (11) being connected to a supporting end piece (13); a mounting couples the supporting end piece which supports the working area; the working area (11) having both a martensitic phase and an austenitic phase depending on a temperature of the instrument; the instrument, in the martensitic phase, being in an inoperative position in which the working area assumes a retracted configuration and is at least partially rectilinear in shape; the instrument, in the austenitic phase, being in a working position in which the working area assumes an expanded structured configuration and being shaped in a shape of the root canal; and once the temperature of the instrument experiences a first predetermined variation, the working area transitions from the martensitic phase to the austenitic phase, and once the temperature of the instrument experiences a second predetermined variation the working area transitions from the austenitic phase to the martensitic phase. 